1. Field of the Invention
This invention relates to a novel liquid crystal substance and a liquid crystal composition containing the same, and more particularly it relates to a chiral liquid crystal substance having an optically active group and a chiral liquid crystal composition containing the same.
2. Description of the Prior Art
As to liquid crystal display elements, TN type display mode has now been most widely employed, but TN type display elements are inferior in response speed to emissive display elements (such as electroluminescence, plasma display, etc.); hence various improvements therein have been attempted and nevertheless it does not appear that a large extent of improvement has been obtained. Thus, various liquid crystal display devices based on a different principle, in place of TN type display elements have been attempted, and among them there is a display mode utilizing a ferroelectric liquid crystal (N. A. Clerk et al, Applied Phys. lett., 36, 899 (1980)). This mode utilizes the chiral smectic C phase (hereinafter abbreviated to S.sub.C * phase) or the chiral smectic H phase (hereinafter abbreviated to S.sub.H * phase), and it is preferred that such phases be present in the vicinity of room temperature.
Certain compounds used for such applications have already been known. The present inventors, too have filed patent applications directed thereto. For example, EP-110299 discloses a compound expressed by the formula ##STR2## wherein R.sub.11 represents an alkyl group or an alkoxy group; R* represents an optically active group; and m and n each represent 0 or 1.
EP-115693 discloses a compound expressed by the formula ##STR3## wherein R.sub.11, R*, m and n are as defined above.
EP-168414 discloses a compound expressed by the formula ##STR4## wherein R*, R.sub.11, m and n are nearly as defined above.
The present inventors have further made research on a liquid crystal substance suitable for utilizing the chiral smectic phase of these ferroelectric liquid crystals, and as a result have found that the above compounds of formulas (A), (B) or (C) but whose benzene ring is substituted by a halogen atom, particularly a fluorine atom as a lateral substituent have superior characteristics to those of formulas (A), (B) or (C).